A modelling approach to infer the solar wind plasma parameters upstream of Mercury from magnetic field observations

Transcription

1 A modelling approach to infer the solar wind plasma parameters upstream of Mercury from magnetic field observations S. Fatemi 1, ( N. Poirier 2, M. Holmström 1, J. Lindkvist 3, M. Wieser 1, S. Barabash 1 1. Swedish Institute of Space Physics, Kiruna, Sweden 2. École Nationale Supérieure de Mécanique et d Aérotechnique, France 3. Umeå University, Umeå, Sweden 52nd eslab symposium ESA/ESTEC,

2 BepiColombo is getting ready for launch! BepiColombo is a Joint ESA/JAXA mission to Mercury BepiColombo configuration: - Mercury Planetary Orbiter (MPO) - Mercury Magnetospheric Orbiter (MMO) - Mercury Transfer Module (MTM) - Sunshield (MOSIF) Launch: Oct 2018 One Earth flyby: 2020 Two Venus flybys: 2020, 2021 Five Mercury flybys: Arrival: Dec 2025 for one year 1

3 IRF sensors on BepiColombo - Miniature Ion Precipitation Analyzer (MIPA) on MPO/SERENA - Energetic Neutral Analyzer (ENA) on MMO/MPPE 2

4 Mercury - Average radius is 2440 km 38% of the Earth radius 93% of Ganymede (a Galilean moon), 0.95% of Titan (a Saturnian moon) - Exosphere (Na, Ca, K, H, He, Mg, and perhaps O and Al) The most dominant ion species is Na + with density ~ cm -3 - Mercury has a very large metallic core (0.8 R) Ganymede Mercury Venus Earth Mars 3

5 Global magnetic field Mercury has a weak global, intrinsic magnetic field that supports a small magnetosphere. Surface fields strength [ut] Tilt from rotational axis [deg] Central offset [h/r] Dipole moment Mercury ~0.2 < South Earth ~35 ~ South Jupiter ~430 ~10 Small! (JUNO!) North Courtesy of C. Arridge, F. Bagenal and S. Bartlett. 4

6 Solar wind interaction with Mercury - Bow shock: ~1.9 RM - Magnetopause: ~1.4 RM - Most of the magnetosphere is filled by the planet itself - Mercury s mini-magnetosphere is highly dynamic and responsive to the solar wind and magnetic field variations: Dungey cycle Earth: ~1 h Mercury: ~2 min Reconnection rate Earth: ~0.05 Mercury: ~0.15 [Slavin et al., 2009] 5

7 A challenge for observations! The lack of an upstream solar wind plasma monitor when a spacecraft is inside the dynamic magnetosphere of Mercury limits interpretations of observed magnetospheric phenomena and their correlations with upstream solar wind variations. It is important to separate the internal and external magnetic fields. What are the solar wind plasma parameters when a spacecraft is inside the magnetosphere? Different methods have been applied [stp.isas.jaxa.jp] For example - Winslow et al., 2013 used WSA-ENLIL model - Slavin et al., 2014 used pressure balance 6

8 AMITIS: A GPU-based hybrid model of plasma Inverse problem approach using a hybrid plasma model - AMITIS: a 3D hybrid model of plasma (kinetic ions and fluid electrons) - Runs on a GPU (Graphical Processing Unit): <=1 day for one simulation - Well-tested against several observations - Implicit solver for the interior coupled with an explicit plasma solver ~10x faster than a CPU-based hybrid model using ~380 CPUs! [Fatemi et al., 2017] 7

9 AMITIS: A GPU-based hybrid model of plasma Inverse problem approach using a hybrid plasma model - AMITIS: a 3D hybrid model of plasma (kinetic ions and fluid electrons) - Runs on a GPU (Graphical Processing Unit): <=1 day for one simulation - Well-tested against several observations - Implicit solver for the interior coupled with an explicit plasma solver ~10x faster than a CPU-based hybrid model using ~380 CPUs! The only known parameter: Magnetic field (MESSENGER/MAG) Magnetospheric boundaries are also known from MAG observations. [Fatemi et al., 2017] A range of the solar wind plasma parameters 7 [Winslow et al., 2013]

10 MESSENGER magnetic field observations BS: bow shock MP: magnetopause CA: closest approach 2011; DOY 113 Known parameters: - One hour averaged (Bx, By, Bz) = (-10.7, +15.4, +0.5) nt - Magnetospheric boundaries 8

11 MESSENGER magnetic field observations BS: bow shock MP: magnetopause CA: closest approach Solar wind plasma: n sw : : 2 /cm3 v sw : : 10 km/s Ti = Te = 12 ev Total: 48 simulations No exosphere No conductive core 2011; DOY 113 Known parameters: - One hour averaged (Bx, By, Bz) = (-10.7, +15.4, +0.5) nt - Magnetospheric boundaries 8

12 Comparison with MESSENGER (2011/113) n_sw = 22 /cm^3 v_sw = 300 km/s Pdyn = 3.6 npa MA = 3.6 Beta = 0.28 Current density [Fatemi et al., 2018; A&A] 9

13 Inferred plasma parameters by AMITIS Inbound Outbound Bow shock [npa] Magnetopause [npa] 2.7± ± ± ±0.5 [Fatemi et al., 2018; A&A] WSA-ENLIL: ~7 npa 10

14 Global view of the interaction (2011/113) 11

15 Magnetopause response Magnetopause response [Winslow et al., 2013]: [Winslow et al., 2013] 12

16 Magnetopause response Magnetopause response [Winslow et al., 2013]: [Winslow et al., 2013] [Slavin et al., 2014] 12

17 Magnetopause response [Fatemi et al., 2018; A&A] 13

18 Magnetopause response [Fatemi et al., 2018; A&A] What is the role of the core? 13

19 Summary - We have developed a tool to estimate the solar wind plasma parameters upstream of Mercury based on magnetic field observations. - Our model estimates the location of Mercury s magnetospheric boundaries quiet accurately! - We have successfully validated our simulations against MESSENGER. - We can run similar campaigns for every orbit of BepiColombo and MESSENGER, as long as the IMF remains relatively constant before and after the bow shock crossing. Future work: - MIPA and ENA response in the magnetosphere - Mercury s core and plasma interaction! 14

20

21 MESSENGER orbit selections - A few well-studied orbits The selected orbits cover different magnetospheric regions! The only known parameter: magnetic field (MAG) 1h average of the B-field [Fatemi et al., 2018; submitted] 5

22 (D182) MAG observations 11

23 Comparison [Fatemi et al., 2018; A&A] 13

24 Global view of the interaction (D182) Our model estimated P dyn ~7.5 npa WSA-ENLIL predicted P dyn ~10.5 npa 12

25

26 Another model results ~50 nt [Richer et al., 2012] 10